Crystalline MnO 2 exhibits excellent photo-thermal conversion and adjustability of valence states properties, but the weak near-infrared light absorption, poor charge transportation and utilization limit its environmental applications. Herein, a novel Na-doped amorphous MnO 2 /C-decorated Fe-based geopolymer sphere (A-MnO 2 /C-FeGS) with rich structure vacancies was constructed by ion exchange anchoring strategy and used to degrade tetracycline hydrochloride (TC) in solar light-induced photo-thermal-Fenton process. Manganese residue (MR), an industrial solid waste, was used as the source of Fe and Si. A-MnO 2 /C-FeGS exhibited excellent catalytic performance with TC removal of 98.2% within 30 min, being about 4.5 and 3.3 times faster than crystalline MnO 2 and C-FeGS, respectively. The improved photocatalytic activity was attributed to that rich oxygen vacancies could provide more catalytic active sites and accelerate Fe 3+ /Fe 2+ and Mn 4+ /(Mn 2+ +Mn 3+ ) conversion for more ·OH generation. Moreover, Na-doped amorphous MnO 2 and C decoration synergistically contributed to high photo-thermal conversion rate, which could in-situ heat the catalyst and induce the activation of H 2 O 2 . This promoted the activation of the surface lattice oxygen and accelerated the secondary transition and utilization of the thermal electrons captured by the defect sites. This work provides a novel strategy for the development of highly reactive catalysts and valorization of MR in the field of environmental remediation.
Constructing bimetallic nanostructures with specific crystalline phases provides an attractive strategy to develop highly efficient catalysts and explore structure-dependent catalytic properties. Herein, a new iron-based bimetallic catalyst consisting of amorphous MnO 2 and crystalline α-Fe 2 O 3 was synthesized for peroxymonosulfate (PMS) activation, named as a-MnO 2 /α-Fe 2 O 3 . The results show that the removal efficiency of sulfamethoxazole is over 90% within 120 min by the a-MnO 2 /α-Fe 2 O 3 in the presence of PMS at broad pH conditions ranging from 3 to 9. Furthermore, a complete degradation of bisphenol A (BPA) is achieved within 2 min in the a-MnO 2 /α-Fe 2 O 3 /PMS system under optimum conditions, and the BPA degradation rate constant of 1.67 min −1 outperforms most reported Fe- and Mn- based catalysts. The results of electron paramagnetic resonance analysis, quenching tests and Raman spectroscopy analysis show that the mechanism for the a-MnO 2 /α-Fe 2 O 3 -based PMS activation is dominated by the formation of activated surface-PMS complexes. ≡Mn(Ⅳ)–OH and ≡Fe(III)–OH of a-MnO 2 /α-Fe 2 O 3 are active sites for PMS adsorption to form inner-sphere complexes (≡Mn(Ⅳ)-OOSO 3 - ) through the replacement of surface hydroxyl groups. Finally, the a-MnO 2 /α-Fe 2 O 3 exhibits a remarkable removal efficiency of over 99% for BPA in column-bed tests conducted over 600 cycles, demonstrating its immense potential for practical applications.
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